KR101588858B1 - A Method of Hologram Watermarking Using Fresnel Diffraction Model - Google Patents

Abstract

The present invention relates to a hologram watermarking method based on a Fresnel diffraction model, which is to process a digital hologram to generate a diffraction pattern in a two-dimensional (2D) form by using Fresnel transformation, to perform the Fresnel transformation again on the hologram so as to generate a watermark area around an image, and to insert the watermark undergone the Fresnel transformation into the watermark area and extract the same. The hologram watermarking method comprises the steps of: (a) obtaining a complex image by applying Fresnel transformation to a digital hologram image; (b) transforming the complex image into a polar-form image, and generating a magnitude image in a 2D form consisting of magnitude components in the polar-form image; (c) applying the Fresnel transformation to the magnitude image so as to obtain an transformed image; (d) inserting a watermark into the transformed magnitude image; (e) performing inverse Fresnel transformation on the transformed magnitude image into which the watermark is inserted so as to restore the magnitude image; (f) reconstituting the polar-form image with the restored magnitude image and transforming the polar-form image reconstituted into the complex image so as to restore the image; and (g) restoring the complex image restored to a digital hologram image via inverse Fresnel transformation so as to obtain a hologram image into which the watermark is inserted. By the hologram watermarking method stated above, the watermark insertion area is inserted after being enlarged to surrounding areas using Fresnel transformation properties, thus the inserted watermark can have enough invisibility and be resilient against general image-processing attacks such as Gaussian blur, sharpening, image compression and the like.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a holographic watermarking method based on a Fresnel diffraction model,

The present invention generates a 2D diffraction pattern using a Fresnel transformation of a digital hologram, performs a Fresnel transformation again on the 2D hologram, generates a watermark area on the periphery of the image, And a hologram watermarking method based on Fresnel diffraction model for inserting and extracting watermarks subjected to Fresnel transformation.

Digital hologram technology records the interference phenomenon between a reference light wave used as a light source and an object light wave reflected on an object into a CCD (Charge Coupled Device) instead of a hologram film. In order to restore the hologram recorded through the CCD, the hologram is loaded into the SLM (Spatial Light Modulator) and the reference wave of the same wavelength is irradiated, thereby restoring the object at the same distance as when recording.

Since the hologram contents are very expensive contents from the recording devices, researches on watermarking by various research teams have been going on [Non-Patent Documents 7-11].

Of the general image watermarking techniques, techniques in which the watermark application domain is a frequency domain have characteristics that are more resistant to attacks than spatial domains (Non-Patent Document 4-6). However, this corresponds to a general two-dimensional (2D) -based image, and the high frequency region is much larger than the two-dimensional (2D) image due to the characteristics of the hologram image. Therefore, it is difficult to apply the watermarking technique used in a general two-dimensional (2D) image to a hologram.

Since the hologram has information about the light source and parameters of optical equipments such as pixels of the CCD, researches have been carried out using the watermarking technique using it [Non-Patent Documents 7-9]. In addition, the hologram has been changed to the frequency domain, and the watermarking technique used in the 2D region has also been researched by using it [Non-Patent Document 10] [Non-Patent Document 11].

[Non-Patent Document 1] HILAIRE, PIERRE ST, "HOLOGRAPHIC VIDEO: The ultimate visual interface?", Optics and Photonics News, Vol. 8 Issue 8, pp. 35- (1997). [Non-Patent Document 2] J. K. Chung and M. H. Tsai, "Three-Dimensional Holographic Imaging", John Wiley & Sons, [Non-Patent Document 3] S.A. Benton and V. M. Bove Jr. "Holographic Imaging ", John Wiley & Sons, Inc., Hoboken, NJ, 2008. [Non-Patent Document 4] J. O. Ruanaidh, W. J. Dowling, and F. M. Boland, "Phase Watermarking of Digital Image," in Proc. ICIP'97, Vol.1, pp.239-242, Sep., 1996. [Non-patent Document 5] IJ Cox, J. Kilian, FT Leighton, and T. Shamoon, "Secure Spread Spectrum Watermarking for Multimedia," IEEE Transactions on Image Processing, Vol.6, pp. 1673-1687, Dec., 1997 . [Non-Patent Document 6] M. Barni, "Image Watermarking of Secure Transmission over Public Networks," Proceedings of COST 254 Workshop on Emerging Techniques for Communication Terminals, Toulouse, France, pp. 290-294, Jul. [Non-Patent Document 7] C. J. Chen, L. C. Lin, W. T. Dai, "Consturction and detection of digital holographic watermarks", Optics Communications, Vol.248, pp. 105-116, Sep. 2005. [Non-Patent Document 8] Kishk S, Javidi B. 3D object watermarking by a 3D hidden object. Opt Express 2003; 11 (8): 874-108. [Non-Patent Document 9] Kim H, Lee YH. Optimal watermarking of digital hologram of 3-D object. Opt Express 2005; 13 (8): 2881-6. [Non-Patent Document 10] H.-J. Choi, Y.-H. Seo, J.-S. Yoo, and D.-W. Kim, "Digital watermarking technique for holography interference patterns in a transform domain ", Optics and Lasers in Engineering, Vol. 46, Issue 4, pp 343-348, April 2008. [Non-Patent Document 11] H. J. Choi, Y. H. Seo, J. S. Yoo, D. W. Kim, "HoloMarking: Digital Watermarking Method using Fresnel Hologram", The Korean Instute of Communications and Information Sciences, Vol. 34, No. 6, pp. 604-610, Jun. 2009. [Non-Patent Document 12] Fresnel Diffraction, "http://en.wikipedia.org/wiki/Fresnel_diffraction".

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and it is an object of the present invention to provide a method and apparatus for reconstructing a two-dimensional (2D) image using a characteristic of Fresnel transformation, And a hologram watermarking method based on a Fresnel diffraction model for inserting a watermark into a hologram image.

In addition, a digital hologram is generated by generating a two-dimensional (2D) diffraction pattern using Fresnel transformation, and then Fresnel transformation is performed to generate a watermark region around the image, And a hologram watermarking method based on Fresnel diffraction model for inserting and extracting a watermark obtained by performing Fresnel transformation on a mark area.

According to an aspect of the present invention, there is provided a hologram watermarking method based on a Fresnel diffraction model for inserting a watermark into a digital hologram image, the method comprising: (a) acquiring a complex image by applying Fresnel transform to a digital hologram image; ; (b) transforming the complex-valued image into an extreme-type image, and generating a two-dimensional-sized image composed of magnitude components in the extreme-type image; (c) applying a Fresnel transform to the size image to obtain a diffraction pattern image; (d) inserting a watermark into the diffraction pattern image; (e) performing inverse Fresnel transform on the watermark-embedded diffraction pattern image to reconstruct a magnified image; (f) transforming the reconstructed polarized image into a complex number image by reconstructing the polarized image with the reconstructed size image; And (g) reconstructing the reconstructed complex image into a digital hologram image through inverse Fresnel transform to obtain a watermarked hologram image.

Further, in the hologram watermarking method based on the Fresnel diffraction model, the present invention is characterized in that, in the step (d), a Fresnel transform is applied to the watermark, and the transformed watermark is inserted.

The present invention is characterized in that in the hologram watermarking method based on the Fresnel diffraction model, the Fresnel transform is repeatedly applied to the watermark a predetermined number of times.

Further, in the hologram watermarking method based on Fresnel diffraction model, the watermark is embedded in the periphery of the diffraction pattern image in step (d).

Further, the present invention is a hologram watermarking method based on Fresnel diffraction model, characterized in that, in the step (d), the watermark is inserted after diagonal movement.

According to another aspect of the present invention, there is provided a hologram watermarking method based on Fresnel diffraction model, comprising the steps of: (h) acquiring a complex image by applying Fresnel transform to the inserted digital hologram image; (i) transforming the complex-valued image into an extreme-type image, and generating a two-dimensional-sized image composed of magnitude components in the extreme-type image; (j) obtaining a diffraction pattern image by applying Fresnel transform to the magnitude image; And (k) extracting a watermark from the diffraction pattern image.

As described above, according to the hologram watermarking method based on the Fresnel diffraction model according to the present invention, by inserting the watermark embedding area into the surrounding area by using the Fresnel transforming property, the inserted watermark has sufficient invisibility And it is possible to insert a strong watermark against general image processing attacks such as Gaussian blurring, sharpening and image compression.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a configuration of an overall system for carrying out the present invention; Fig.
2 is a diagram illustrating Fresnel transformation characteristics of a 2D image used in the present invention.
FIG. 3 is an exemplary image of a Fresnel transformed result of a 2D image according to the present invention. FIG. 3 (a) shows an original image and a distance of 1.5 m, , (e) An example of a result image at 3 m.
FIG. 4 is an exemplary image of a Fresnel transformed result of a hologram image according to the present invention. FIG. 4 (a) shows a depth image of an object, (b) (D) 50 cm, (e) 100 cm, and (f) 150 cm, respectively, of the result image and the complex number.
5 is a flowchart illustrating a hologram watermarking method (watermark embedding method) based on the Fresnel diffraction model according to the first embodiment of the present invention.
6 is a detailed flowchart illustrating a hologram watermarking method (watermark embedding method) based on the Fresnel diffraction model according to the first embodiment of the present invention.
FIG. 7 is an exemplary image of a watermark embedding result according to the present invention. FIG. 7 is a diagram illustrating an example of watermark embedding result according to the present invention. Referring to FIG. 7, Fig.
8 is a flowchart illustrating a hologram watermarking method (watermark extraction method) based on a Fresnel diffraction model according to a second embodiment of the present invention.
9 is a detailed flowchart illustrating a hologram watermarking method (watermark extraction method) based on a Fresnel diffraction model according to a second embodiment of the present invention.
FIG. 10 is an exemplary image of a resultant image obtained by extracting a watermark according to the present invention, as a result of (a) polar pattern conversion, (b) diagonal movement, and (c) watermark extraction.
FIG. 11 is an exemplary image of a restoration result after watermark embedding according to an experiment of the present invention, wherein the watermarking distances a, b, c, d, ) 74 is an example of a result image.
(A) 62, (b) 65, (c) 67, (d) 70 (e) 72, and (f) 74 in the watermark extraction result as an example image of the watermark extraction result according to the experiment of the present invention. Fig. 8 is a diagram illustrating an example of a resultant image when the image is displayed.
13 is a table showing a comparison between an original hologram and an attacked hologram according to the experiment of the present invention.
FIG. 14 is an exemplary image of a restoration result after various attacks according to an experiment of the present invention as an example of a resultant image for an attack of (a) original, (b) blurring, (c) sharpening, and (d) JPEG compression.
FIG. 15 shows an example of a result image of a watermark extraction result after various attacks according to the experiment of the present invention as a result of (a) original, (b) blurring, (c) sharpening, Degree.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings.

In the description of the present invention, the same parts are denoted by the same reference numerals, and repetitive description thereof will be omitted.

First, examples of the configuration of the entire system for carrying out the present invention will be described with reference to Fig.

1, a method of hologram watermarking based on a Fresnel-Diffraction Model according to the present invention includes the steps of inputting a digital hologram (or a hologram image) 10 and inputting a watermark in the digital hologram, System. ≪ / RTI > That is, the hologram watermarking method can be implemented by a program and installed in the computer terminal 20 and executed. A program installed in the computer terminal 20 can operate as a single program system 30. [

Meanwhile, as another embodiment, the hologram watermarking method may be implemented by a program, and may be implemented by an electronic circuit such as an ASIC (on-demand semiconductor) other than the general-purpose computer. Or a dedicated terminal 30 that exclusively processes only the work of inserting the watermark into the digital hologram. This is called a holographic watermarking apparatus. Other possible forms may also be practiced.

Next, before explaining the hologram watermarking method based on the Fresnel diffraction model according to the present invention in detail, the Fresnel diffraction model used in the present invention will be described with reference to FIG. 2 to FIG.

In order to recover the digital hologram, the interference pattern acquired through the CCD (Charge-Coupled Device) camera is loaded into the SLM (spatial light modulator) and restored. At this time, the reference wave is restored by the diffraction phenomenon of the hologram displayed on the SLM. The equation that mathematically models this diffraction phenomenon is Fresnel transformation [Non-Patent Document 12].

는 하나의 점광원으로부터 z만큼 떨어진 평면에서의 x,y좌표의 회절에 의한 밝기이다. k는 파수로 2π/λ이고, λ는 점광원에 파장으로 홀로그램에 사용한 레이저의 파장과 같다. r은 하나의 점광원으로부터 x,y,z까지 실제 거리로

이다[비특허문헌 12]. Equation (1-5) is a process for obtaining an equation for a Fresnel transformation from one point light source. In Equation (1), E (u, v, 0) in the electric field equation corresponds to the coordinates of one point light source

Is the brightness due to the diffraction of the x, y coordinates in the plane separated by z from one point light source. k is the wave number 2π / λ, λ is the wavelength of the point light source and is equal to the wavelength of the laser used in the hologram. r is the actual distance from one point source to x, y, z

[Non-Patent Document 12].

[Equation 1]

으로 나타낼 수 있다. 만약 λ≪z, λ≪ρ, ρ≪z 를 만족할 경우 이를 프레넬(Fresnel) 영역이라 하고 프레넬(Fresnel) 근사 화를 수행할 수 있다[비특허문헌 12]. 수학식 2와 같이 r은 테일러(Taylor) 급수를 통하여 나타낼 수 있는데 위 가정을 통하여 3차 항 이후는 생략하여 수학식 3과 같이 나타낼 수 있다[비특허문헌 12].From the above, r is obtained through ρ ² = (xu) ² + (yv) ²

. If λ << z, λ <<ρ, and ρ «z are satisfied, it can be called a Fresnel domain and Fresnel approximation can be performed [Non-Patent Document 12]. As shown in Equation (2), r can be expressed through Taylor's series, and the third term can be omitted from Equation (3) through the above assumption (Non-Patent Document 12).

&Quot; (2) &quot;

&Quot; (3) &quot;

로 대체하면 수학식 5와 같이 푸리에 변환 형태로 나타낼 수 있다[비특허문헌 12]. Equation (3) is substituted into Equation (1) and summarized in Equation (4). In this case,

Can be expressed in the form of Fourier transform as shown in Equation (5) [Non-Patent Document 12].

&Quot; (4) &quot;

&Quot; (5) &quot;

Next, the characteristics of the discrete Fresnel transform will be described.

In order to apply the Fresnel transform to the digital hologram, Equation (4) can be discretized as shown in Equation (6). du, dv is the size of the pixel of the light source, and dx and dy are the sizes of the pixels in the diffraction plane.

&Quot; (6) &quot;

로 대체하면 수학식 5와 같이 이산 푸리에 변환 식으로 나타낼 수 있다. 이처럼 λ와 광원의 해상도(N,M)는 고정되어 있는 값이기 때문에 광원의 화소와 회절 평면의 화소의 크기는 거리에 따라서 반비례 관계이다. 이 관계는 2D 영상에 프레넬(Fresnel) 변환을 적용할 경우 에너지가 가운데로 모이는 중요한 특성의 요소인데 이하에서 보다 구체적으로 설명하도록 한다.
In Equation (6)

Can be represented by a discrete Fourier transform equation as shown in Equation (5). As λ and the resolution (N, M) of the light source are fixed values, the size of the pixel of the light source and the size of the pixel of the diffraction plane are inversely proportional to the distance. This relationship is an important feature of the energy gathering in the middle when Fresnel transform is applied to the 2D image, which will be described in more detail below.

Next, the Fresnel transform characteristic of the 2D image will be described in detail.

2 schematically shows a diffraction plane spaced by z in the plane of the 2D image. The 2D image is plane and parallel to the diffraction plane. Therefore, a 2D image can be seen as a planar light source. Therefore, the diffraction pattern of the diffraction plane distant from the 2D image by z appears in a size similar to that of the 2D image. However, the sizes of the pixels of the 2D image plane and the diffraction pattern are different depending on the wavelength, distance, and size of the image according to the relational expression in Equation (7). Therefore, the actual size of the N × M diffraction plane is different. The square (a) of FIG. 2 shows the case where the size of the pixel of the diffraction plane is larger than the pixel size of the image plane and (c) is smaller. The square (b) is the area where the actual diffraction pattern is generated.

&Quot; (7) &quot;

FIG. 3 shows the Fresnel transformation on the 2D image according to the distance. The wavelength of the light source is 633 mm, the 2D image is 1,024 × 1,024, and the pixel size is 24.86 μm, which is equal to the pixel size of the diffraction plane at 1 m. 3 (a) shows an input image, and (b) shows a diffraction plane spaced by a distance of 1 m, 1.5 m, 2 m and 3 m, respectively. In the case of the above distance, the size of the pixel in the diffraction plane is 24.86 μm, 37.30 μm, 49.73 μm, and 74.60 μm, respectively, according to the relational expression.

Next, the Fresnel transform characteristic of the hologram will be described.

When the hologram is restored by using the optical device, the image remains at the generated distance. This is because the actual distance, not the plane, such as the Fresnel transformation, when the Fresnel transformation is applied, the focus is matched when the distance and the diffraction plane coincide with each other, And thus a de-focusing phenomenon occurs. This is shown in FIG. 4 (a) is a depth image for generating a hologram. FIG. 4 (b-c) shows the complex number of the transformed result in the real part and the imaginary part of the Fresnel transformed result. FIG. 4 (bc) is a Fresnel-transformed hologram obtained by adjusting the distance to 110 cm. FIG. 4 (df) shows Fresnel transforms corresponding to 50 cm, 110 cm and 150 cm, It is the image obtained the size.

FIG. 4 is an exemplary image of a Fresnel transformed result of a hologram image according to the present invention. FIG. 4 (a) shows a depth image of an object, (b) (D) 50 cm, (e) 100 cm, and (f) 150 cm, respectively, of the result image and the complex number.

Next, a hologram watermarking method based on the Fresnel diffraction model according to an embodiment of the present invention will be described with reference to FIGS. 5 to 10. FIG.

First, a watermark embedding method will be described.

We have previously discussed the results of applying Fresnel transforms to holograms and 2D images. First, applying Fresnel transformation to the hologram results in real and imaginary parts. If the hologram is transformed into a polarized (magnitude and phase) shape, the image can be reconstructed as a 2D image. When the Fresnel transformation is performed again by adjusting the parameters of the 2D reconstruction result to be smaller in the pixels of the diffraction plane, a phenomenon of centering occurs. At this time, the periphery that does not converge to the center becomes the watermark embedding area, and is inserted again through the inverse Fresnel transform.

As shown in FIG. 5, the Fresnel diffraction model-based hologram watermarking method (watermark embedding method) according to the first embodiment of the present invention includes (a) a complex number image acquiring step S11, (b) (C) a Fresnel transform step S13 of the magnified image, (d) a watermark embedding step (S14) on the transformed magnitude image, (e) a reconstructing step (S15) of the transformed magnitude image, (f) a complex image restoring step (S16), and (g) a digital hologram image restoring step (S17).

6 is a detailed flowchart of a watermark embedding method of the hologram watermarking method based on the Fresnel diffraction model according to the present invention.

First, Fresnel transform is applied to the digital hologram image to obtain a complex image (S11). That is, when a Fresnel transform is applied to the digital hologram image, an image (or a complex image) for the real part and the imaginary part is respectively generated. The Fresnel transform at this time applies a forward Fresnel transform.

Next, the acquired complex image is transformed into a polar image. The polarized image is transformed into a magnitude and a phase, and a two-dimensional image composed of magnitude components, that is, a magnified image of a polarized type is generated (S12).

Next, a Fresnel transform (or forward Fresnel) is applied again to the 2D size image to obtain a transformed size image (or a diffraction pattern image) (S13).

When performing Fresnel transform, there is a plane of each input and output. There is a size of each pixel of each plane. There are also parameters such as the wavelength and distance of the reference wave. This is a necessary parameter for optical reconstruction and generation, and can be properly restored by using the parameters used at the time of creation. When reconstructing a 2D shape, the parameters used to generate the hologram should be used. In order to maintain the invisibility when inserting the watermark, the user must arbitrarily insert parameters other than the parameters used for generation.

If the size of the input hologram (image) is N x N, the size of the output hologram is also N x N. By varying the size of the input and output pixels, the size of the diffraction pattern represented by the same size of N × N is different. 2 for the description of the contents. Actually, if the image is restored by optics (not Fresnel transform), the same size (actual size) pattern appears. If the size of the output pixel is different, the actual size of N × N is also different. Actual size = (N × pixel size) × (N × pixel size).

Next, a watermark is inserted in the periphery of the converted size image (or the diffraction pattern image) (S14).

The generation of the watermark is an input arbitrarily set by the user. The Fresnel transform is performed with a parameter different from the Fresnel transform (to be applied to the hologram) for restoring it, and the transformed result is synthesized.

Further, the Fresnel transform is repeated N times for the watermark. The number of iterations N for repetitive Fresnel transforms is determined at the time of insertion. The repetition of the Fresnel transformation of the watermark is intended to allow the watermark to be completely hidden when viewing (restoring) the hologram.

On the other hand, when the Fresnel transform is performed, a normal 2D (two-dimensional) image is gathered in the center. The degree of gathering varies depending on distance (or distance parameter). Therefore, when the watermark is converted to Fresnel, it is collected in the center.

Also, since the two-dimensional size image is Fresnel-transformed, the diffraction pattern image is also collected in the center. At this time, if the watermark is directly synthesized (added) to the diffraction pattern, a watermark appears when optical or reconstruction is performed. In order to prevent this, the watermark is diagonally moved to the periphery to perform synthesis.

Next, the magnitude image is reconstructed by performing an inverse Fresnel transform on the transformed magnitude image (or the diffraction pattern image) into which the watermark is inserted (S15). Then, the reconstructed polarized image is reconstructed as a complex-valued image (S16). The reconstructed complex image is reconstructed into a digital hologram image through inverse Fresnel transform (S17).

FIG. 7 shows an image for the watermark process. 7 (a) is an image corresponding to the size of the image obtained by performing the Fresnel transformation of the hologram and converting the hologram into the polar expression. 7 (b), the watermarks converge in the center as the watermark is subjected to the N-th Fresnel transformed image. 7 (c) is an image synthesized after diagonal movement of FIGS. 7 (a) and 7 (b). FIG. 7 (e) shows a hologram created by performing inverse Fresnel transformation on the synthesized image, It is a video.

Next, a watermark extraction method will be described.

After performing the Fresnel transformation, the hologram with the watermark is deformed into an extreme form, and only Fresnel transformation of the hologram is performed. At this time, Fresnel transformation is performed by using the distance and wavelength used for insertion and the size of the same pixel. After creating the diffraction pattern, the object moves to the watermark area and the watermark area moves to the center again. You can extract the watermark by performing the inverse Fresnel transform that you used when inserting.

8, a hologram watermarking method (particularly a watermark extraction method) based on a Fresnel diffraction model according to a second embodiment of the present invention includes (a) a complex number image acquiring step S21, (b) (C) a Fresnel transformation step (S23) of the magnified image, and (d) a watermark extraction step (S24) from the converted magnitude image.

9 is a detailed flowchart of a watermark extraction method of the hologram watermarking method based on the Fresnel diffraction model according to the second embodiment of the present invention.

First, a Fresnel transform is applied to a digital holographic image in which a watermark is embedded to obtain a complex image (S21). Then, the obtained complex-valued image is transformed into a polarized image, and a two-dimensional image composed of magnitude components among the polarized components is generated (S22). Then, the Fresnel transform is applied again to the 2D size image, and the converted size image is obtained (S23).

Next, a watermark is extracted from the converted size image (S24).

As described above, when a watermark is synthesized on a diffraction pattern image, the watermark is shifted diagonally to the periphery to perform synthesis. Therefore, in order to extract again, the watermark in the peripheral part is shifted to the central part, and the backward Fresnel transform is performed.

On the other hand, in generating the watermark, the inverse Fresnel transform is repeatedly performed a number of times that the frame transform is repeated, thereby extracting the watermark.

Fig. 10 shows an intermediate image of the watermark extraction process. Fig. 10 (a) shows the magnitude component of the polarized expression, and Fig. 10 (b) shows the image subjected to the diagonal movement. 10 (c) is a watermark image extracted by performing Fresnel transform.

Next, the effects of the present invention through experiments will be described in more detail with reference to FIGS. 11 to 15. FIG.

First, the watermark insertion distance will be described.

FIG. 11 shows a result obtained by inserting a watermark in accordance with a distance when performing Fresnel transform of a watermark and restoring it. The result of FIG. 11 is a process of pre-processing the values so that the average value is '0' during the Fresnel transform for restoration in order to eliminate the DC region generated when the watermark is restored.

FIG. 12 is a watermark extracted when extracting at a distance as shown in FIG. 11, noise occurring in the DC region occurs during the process of inserting a watermark, and when the distance of the Fresnel transform applied to the watermark is short, the degree of watermark gathering becomes small and a phenomenon of overlapping with the object region occurs . In this case, the watermark area may be greatly damaged by the object having a relatively large value. Conversely, when the distance is too long, the degree of convergence increases, so the size of the object is smaller than that of the object, which also causes damage to the watermark. 11 and 12 increase the watermarking distance in order.

Next, the robustness of the watermark according to the experiment of the present invention will be described.

The table in Fig. 13 shows the PSNR with hologram before insertion after watermark embedding. FIG. 14 shows a reconstructed image when each attack is applied to the table of FIG. When blurring is performed on the hologram, it can be seen that the object part which is important information as shown in FIG. 14 (b) is greatly damaged. Also, it can be seen in Figure 14 (c) that sharpening also causes a lot of noise around the object. As shown in FIG. 14 (d), when compression is applied to a general 2D image, objects are also greatly damaged. FIG. 15 shows that the watermark is extracted after this attack is applied to the hologram inserted with the watermark. (a) is the watermark extracted without attack, and (bd) is the result after performing blurring, sharpening, and JPEG compression, respectively.

In the present invention, a method of generating a 2D diffraction pattern by Fresnel transformation of a hologram and inserting a watermark embedding area into a surrounding area by using the Fresnel transformation property of a 2D image is explained Respectively. As a result of the invisibility test of the method according to the present invention, the inserted watermark satisfies sufficient invisibility, and Gaussian blurring, JPEG compression, and JPEG2000 compression attack are performed for robustness verification. As a result, it was confirmed that the extracted watermark has sufficient visibility.

Although the present invention has been described in detail with reference to the above embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention.

10: digital holographic image 20: computer terminal
30: Program system

Claims (6)

A hologram watermarking method based on a Fresnel diffraction model for inserting watermarks into digital hologram images,
(a) acquiring a complex image by applying Fresnel transform to a digital hologram image;
(b) transforming the complex-valued image into an extreme-type image, and generating a two-dimensional-sized image composed of magnitude components in the extreme-type image;
(c) applying a Fresnel transform to the size image to obtain a diffraction pattern image;
(d) inserting a watermark into the diffraction pattern image;
(e) performing inverse Fresnel transform on the watermark-embedded diffraction pattern image to reconstruct a magnified image;
(f) transforming the reconstructed polarized image into a complex number image by reconstructing the polarized image with the reconstructed size image; And
(g) restoring the reconstructed complex image to a digital hologram image through inverse Fresnel transform to obtain a hologram image with a watermark embedded therein.
The method according to claim 1,
Wherein in the step (d), Fresnel transform is applied to the watermark, and the transformed watermark is inserted.
3. The method of claim 2,
And the Fresnel diffraction model-based hologram watermarking method is repeatedly applied to the watermark by a predetermined number of Fresnel transformations.
The method according to claim 1,
Wherein the watermark is embedded in the periphery of the diffraction pattern image in the step (d).
5. The method of claim 4,
Wherein the watermark is inserted after diagonal movement in the step (d).
A hologram watermarking method based on Fresnel diffraction model for extracting a watermark from a digital hologram image having a watermark inserted by the method according to any one of claims 1 to 5,
(h) acquiring a complex image by applying Fresnel transform to the inserted digital hologram image;
(i) transforming the complex-valued image into an extreme-type image, and generating a two-dimensional-sized image composed of magnitude components in the extreme-type image;
(j) obtaining a diffraction pattern image by applying Fresnel transform to the magnitude image; And
(k) extracting a watermark from the image of the diffraction pattern.

Images